Preface

Ruby is the interpreted scripting language for quick and
easy object-oriented programming. It has many features to
process text files and to do system management tasks (as in
Perl). It is simple, straight-forward, and extensible.

If you want a language for easy object-oriented programming,
or you don't like the PERL ugliness, or you do like the
concept of lisp, but don't like too much parentheses, Ruby
may be the language of the choice.

Ruby's features are as follows:

Interpretive

Ruby is the interpreted language, so you don't have
to recompile to execute the program written in Ruby.

Variables have no type (dynamic typing)

Variables in Ruby can contain data of any type. You
don't have to worry about variable typing. Consequently,
it has weaker compile time check.

No declaration needed

You can use variables in your Ruby programs without
any declarations. Variable name itself denotes its
scope (local, global, instance, etc.)

Simple syntax

Ruby has simple syntax influenced slightly from Eiffel.

No user-level memory management

Ruby has automatic memory management. Objects no
longer referenced from anywhere are automatically collected by the
garbage collector built in the interpreter.

Everything is object

Ruby is the pure object-oriented language from the
beginning. Even basic data like integers are
treated uniformly as objects.

Class, inheritance, methods

Of course, as a O-O language, Ruby has basic features
like classes, inheritance, methods, etc.

Singleton methods

Ruby has the feature to define methods for certain
specified object. For example, you can define a
press-button action for certain GUI button by
defining a singleton method for the button. Or, you
can make up your own prototype based object system
using singleton methods (if you want to).

Mix-in by modules

Ruby does not have the multiple inheritance
intentionally. IMO, It is the source of
confusion. Instead, Ruby has modules to share the
implementation across the inheritance tree. It is
often called the "Mix-in."

Iterators

Ruby has iterators for loop abstraction.

Closures

In Ruby, you can objectify the procedure.

Text processing and regular expression

Ruby has bunch of text processing features like in Perl.

Bignums

With built-in bignums, you can calculate
factorial(400), for example.

Exception handling

As in Java(tm).

Direct access to OS

Ruby can call most of system calls on UNIX boxes. It
can be used in system programming.

Dynamic loading

You can load object files into Ruby interpreter
on-the-fly, on most of UNIXes.